Paint pumps for airless guns at the present time are generally mechanically, hydraulically or pneumatically driven pistons or diaphragms. Each of the driving techniques presently employed has its own problems involving pressure control of the paint to the airless gun. Release of the gun trigger in the course of painting by the operator requires that the paint pump (piston or diaphragm) be prevented from any further pumping action; otherwise, an over-pressure condition will develop.
The mechanically driven pumps heretofore known have employed paint pressure sensitive switches acting on the electric motor driver directly or indirectly through a clutch between the electric motor and the mechanical driver. The pneumatically driven pumps have employed a conventional regulator to limit the maximum pneumatic pressure available to the driver. The hydraulically driven systems heretofore have employed variable displacement pressure compensated hydraulic pumps or relief valves where all or a portion of the hydraulic fluid is metered across the valve to prevent over-pressurization.
The variable displacement pressure compensated pump is the most efficient means since at zero flow the power consumption is at a minimum. Unfortunately, such a pressure compensated system is relatively expensive compared to the constant displacement hydraulic pump with its hydraulic relief valve.